On the possibility of a significant increase in the storage time of ultracold neutrons in traps coated with a liquid helium film

TL;DR

This paper proposes coating ultracold neutron traps with a superfluid helium film to significantly extend neutron storage times by reducing wall absorption, with triangular roughness surfaces being most effective.

Contribution

It introduces a method to coat trap walls with a superfluid helium film thicker than neutron penetration depth, significantly reducing neutron loss.

Findings

Triangular roughness enhances neutron retention more than rectangular.

Helium film coating can reduce neutron loss by orders of magnitude.

Industrial fabrication of diffraction gratings facilitates implementation.

Abstract

It is shown that rough inner walls of a trap of ultracold neutrons can be coated with a superfluid helium film much thicker than the depth of penetration of ultracold neutrons into helium. This coating should reduce the rate of loss of ultracold neutrons caused by absorption in the walls of the trap by orders of magnitude. It is demonstrated that triangular roughness is more efficient than rectangular for the reduction of the rate of loss of ultracold neutrons. Triangular roughness is more easily implemented technically and such diffraction gratings are fabricated industrially. Other methods are proposed to increase the thickness of the protective helium film.